Wolf Tooth Performance Headsets are machined out of aircraft grade aluminum and assembled with Black Oxide Cartridge Bearings balancing quality and price.Black Oxide Bearings are made from chromium steel for high load capacity durability and corrision resistanceUltralight stem cap with integrated spacer plus an aluminum bolt and a star nutO-ring seal prevents water intrusion around the steerer tubeCustom-molded upper lip seal provides additional protection for upper bearingBearing top cap outer diameter: 45.8mm